MILAN (AP) — Survivors described being thrown forward violently and then freeing themselves from a tangle of metal and body parts after two Italian commuter trains collided head-on Tuesday in the southern region of Puglia, killing at least 22 people and injuring scores more.

At least two passengers were pulled alive from the crumpled wreckage as the rescue operation took place in the scorching heat. Premier Matteo Renzi traveled to the scene, where prosecutors and investigators were at work trying to determine why two trains were on a single track.

Railway police Commander Giancarlo Conticchio told Sky TG24 said that the number of dead was 22 with 43 people injured, adding that the numbers could change. Officials stressed the final toll would not be known until the train cars had been pulled apart; a giant crane arrived at the scene to remove the mangled debris.

"Surely one of the two trains shouldn't have been there. And surely there was an error. We need to determine the cause of the error," Conticchio said.

An aerial photo showed the cars crumpled together like an accordion, and forced off the tracks at sharp angles. The two trains, each with four cars, collided head-on in an olive grove on flat terrain between the towns of Andria and Corato. The accident occurred around 11:30 a.m. some 50 kilometers (30 miles) northwest of the Puglia regional capital, Bari.

One elderly couple described their ordeal to local television Telesveva. The man, his head covered in gauze, said he was knocked to the ground, while his wife, still barefoot, described how she came across body parts as she freed him.

"I pulled him from under the debris, myself barefoot, from under the debris and metal," the woman, who was not identified, told local TV. "I went to my husband screaming. I pulled him by the legs and feet. I climbed past people in pieces, how sad. There was nothing I could do.

A woman who is eight months pregnant described being thrown forward.

"I don't know what happened, it all happened so quickly, I don't know," she told The Associated Press. "I saw my mother on the ground, my father and my sister bleeding, I don't know, I don't know, even I don't know."

Another survivor described the scene as "hell."

Corato Mayor Massimo Mazzilli said debris was scattered all over the countryside.

"It's a disaster as if an airplane fell," Mazzilli said on his Facebook page, where he posted photos of the crash.

Premier Renzi pledged a thorough investigation. He returned to Rome from Milan to monitor the situation, and then traveled on to the scene of the accident. His transport minister, Graziano Delrio, as well as local prosecutors were at the scene.

"We must begin to understand the causes of this tragedy that has saddened the whole country," Delrio said at the site, announcing a commission of inquiry. "The crash was certainly violent. Extremely violent."

Pope Francis sent a telegram to the archbishop of Bari, Monsignor Fracnesco Cacucci, saying he shared in the pain of so many families. He said he was mourning those who died and praying for the injured to recover quickly.

The trains were operated by a private, Bari-based rail company, Ferrotramviaria, that connects the city of Bari with Puglia towns to the north and the airport. Ferrotramviaria's website said its fleet comprises 21 electric trains, most with four cars each. The line serves mostly students and commuters.

In a phone interview with state TV, Ferrotramviaria director general Massimo Nitti said the dynamics of what went wrong are still to be determined, but it is clear "one of the trains wasn't supposed to be there" at the same time as the other.

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Winfield reported from Rome. Frances D'Emilio in Rome also contributed.